The present invention relates to an improvement of technology for automotive audio systems. More particularly, the invention relates to the idea of allowing both audio data and a control signal for controlling an external device to be sent over a single common line.
Known in the art are automotive audio systems that are installed on automobiles and other vehicles to reproduce the sound recorded on compact disks (CDs) and other media. A typical automotive audio system consists of a main unit that performs various kinds of control such as selection of a sound source and volume control and an external device such as a CD changer which is connected to the main unit via a bus of the type used in computers.
In this configuration, communication for causing information such as a playback command to be transferred between the main unit and the external device is established via the bus to provide better compatibility for an automotive navigation system and a vehicular computer. When the sound from the external device is to be reproduced with a speaker or the like via the main unit in the prior art automotive audio system, the digital audio data read from a recording medium such as a CD in the external device must first be converted to an analog sound signal or the like before it is sent to the main unit.
FIG. 8 is a functional block diagram showing an exemplary configuration of a CD drive for playback of CDs which is an example of the external device in the conventional automotive audio system. In the illustrated case, a replay command sent from the main unit passes through a bus converter unit 10 and an interface unit 30 to be forwarded to a mechanism control CPU 40. In accordance with the control by the mechanism control CPU 40, a servo processor 50 controls various servo mechanisms including tracking servo, focus servo and spindle servo via a driver 60.
A signal read with an optical pickup is amplified with a RF amplifier 70 and fed back to the servo processor 50. The amplified signal is also sent to a signal processing unit 80, where it is divided into three 20 components, one of which is sent to a signal converter unit 20 and converted to an analog sound signal, which is then output to an analog audio output line. The other components are used for control purposes and sent to the mechanism control CPU 40 and a decoder 90.
When reproducing the sound sent from the external device in the system shown in FIG. 8, the conventional practice is to send from the main unit a command that requests one or more pieces of music at a time and also send the same command to the mechanism control CPU in the external device. To be more specific, when the sound from the external device need be reproduced, the main unit first makes a music replay command that requests one or more pieces of music at a time and sends it to the bus. Upon reception by the external device, the command is sent to the mechanism control CPU 40 via the bus converter unit 10 and the interface unit 30. In response to the single command requesting for music replay that has been sent to the mechanism control CPU 40, one or more pieces of music are reproduced.
In the prior art described above, if a flaw in the medium or some other phenomenon causes an error in the reading of data by the CD driver shown in FIG. 8, the error is corrected by the mechanism control CPU 40 and the mechanisms such as servo processor 50 that are controlled by the CPU (the mechanisms are hereunder collectively referred to as xe2x80x9cplayback meansxe2x80x9d).
However, the prior art technology described above has had various problems. First, the line of a control signal sent from the main unit to control the external device must be provided as a separate and independent entity from the line of sending a sound signal from the external device to the main unit. This inevitably increases the complexity of the overall system configuration.
Second, the conversion of digital audio data to an analog sound signal in the external device requires dedicated means and processing but this introduces deterioration of sound quality compared to the case of transmitting analog sound signals as such.
Third, the main unit receives the sound signal in analog form and, without analog-to-digital conversion, equalizing and other digital processing steps cannot be performed by means of a digital signal processor (DSP) which means considerable difficulty is involved in processing the sound signal.
Another problem with the prior art is that if, during the playback of at least one piece of music in response to the above-described command in the external device, the main unit performs the operation of jumping to next music (commonly called xe2x80x9ctrack-upxe2x80x9d) or getting back to the preceding music (commonly called xe2x80x9ctrack-downxe2x80x9d), a command for temporary stop of replay has to be sent from the main unit to the external device. This is simply because in music reproduction, a playback command that is sent from the main unit to the external device requests for one or more pieces of music to be reproduced; after stopping the playback of music by sending the above-described command for playback stop, a command requesting for replay from the desired location must be sent but then the processing scheme becomes complex.
Sending a replay command that requests for reproduction of one or more pieces of music from the main unit to the external device presents a further problem. If an error such as interruption of data occurs in the playback means in the external device due, for example, to a flaw in the medium (i.e., disk) or its vibration, the error is difficult to correct and considerable difficulty is involved in securing the operational stability of the system.
If the error in the reading of data that has occurred due to a flaw in the medium or by some other reason is to be corrected solely by the replay means, it is difficult for the interface unit, the bus converter unit and the main unit to recognize the error information and perform the corresponding necessary operations, potentially causing a problem in the smooth processing by the system.
The present invention has been accomplished under these circumstances of the prior art and has as an object providing an automotive audio system in which the audio data from an external device is sent to a main unit as it remains in digital form, whereby both audio data and a control signal for controlling the external device are sent over a single common line to simplify the overall system configuration, prevent deterioration of sound quality and facilitating the processing of audio data in the main unit.
Another object of the invention is to provide an automotive audio system in which a command for music replay from the main unit is resolved at equal time intervals in the external device and the resulting small segments of the command are sent to the replay means, thereby increasing the efficiency and stability of the processing in the system.
Yet another object of the invention is to provide an automotive audio system in which an error in the reading of data is corrected in a bus converter unit, whereby the occurrence of the error and the contents of its correction can be recognized in the bus converter unit and the main unit so as to facilitate diverse error correction and stable system operation.
The first object of the invention can be attained by the automotive audio system recited in aspect 1, which comprises a first unit for acquiring a sound signal to be reproduced, a second unit for controlling the first unit by means of a control signal and also reproducing the supplied sound signal, and a bus for establishing communication between the first unit and the second unit, characterized in that the automotive audio system is adapted to transfer the control signal and the sound signal in digital format between the first unit and the second unit via the bus.
The invention recited in aspect 5 is equivalent to the invention of aspect 1, provided that it is expressed as a method of controlling an automotive audio system which comprises the steps of acquiring a sound signal to be reproduced by a first unit, controlling the first unit by means of a control signal and also reproducing the supplied sound signal by a second unit, and establishing communication between the first unit and the second unit by a bus, further comprising the step of transferring the control signal and the sound signal in digital format between the first unit and the second unit via the bus.
The invention recited in aspect 2 is a modification of the automotive audio system of aspect 1 and characterized in that the first unit comprises a bus converter means for controlling the transfer of signals via the bus and a control means for transferring the sound signal via the bus.
The invention recited in aspect 6 is equivalent to the invention of aspect 2, provided that it is expressed as a method of controlling an automotive audio system which is a modification of the invention recited in aspect 5, which further includes the steps of controlling the transfer of signals via the bus in the first unit and transferring the sound signal via the bus in the first unit.
According to the inventions of aspects 1, 5, 2 and 6, the line over which a sound signal is sent from the first unit exemplified by an external device such as a CD changer to the second unit such as a main unit and the line for sending a control signal from the second unit to the first unit can be realized as a single common bus. Namely, the sound signal is transferred from the external device to the main unit as it remains in a digital format. Not only does this obviate the use of two different signal sending lines but the external device also has no need to have a capability by which a digital format of sound signal read from a CD or other medium is converted to an analog format and, as a result, the overall system configuration is simplified. In addition, there is no deterioration in the quality of sound to be reproduced and the processing of the sound signal in the main unit can be facilitated.
The second object of the invention can be attained by the invention of aspect 3 which is a modification of the automotive audio system recited in aspect 1 or 2, wherein the first unit has a playback means for reading a sound signal from a recording medium and the bus converter means has a command resolving means by which a command for reading a predetermined volume of sound signal from a designated address on the recording medium is sent to the playback means at predetermined time intervals in accordance with the contents of the control signal being supplied.
The invention of aspect 7 is equivalent to the invention of aspect 3, provided that it is expressed as a method of controlling an automotive audio system which is a modification of the invention recited in aspect 5 or 6, wherein the first unit has a playback means for reading a sound signal from a recording medium and which further includes a step in which a command for reading a predetermined volume of sound signal from a designated address on the recording medium is sent to the playback means at predetermined time intervals in accordance with the contents of the control signal being supplied.
In the inventions of aspects 3 and 7, when a playback start command is sent from the second unit, the first unit does not forward the supplied command but a command instructing reproduction of each specified block is sent to the playback means at given time intervals. Thus, the second unit has no need to send a stop command to the first unit even if the operation of track-up or track-down is performed during playback. To be more specific, the first unit which has received a signal such as one for track-up needs only to supply the playback means with a command requesting for replay from a re-designated start address. As a result, the processing for the second unit to control the first unit can be performed with increased efficiency.
Even in the case where the second unit performs the operation of stopping playback and a signal to that effect is sent to the first unit, the latter does not have to send another command for playback stop to the replay means but it needs only to stop sending the command requesting for replay. Thus, control procedures such as starting replay, re-designating a start address and stopping replay are all taken within the first unit and any errors that occur in the replay means due, for example, to a flaw in the medium and its vibration can be easily corrected to increase the operational stability of the system.
The third object of the invention can be attained by the invention of aspect 4 which is a modification of the automotive audio system recited in any one of aspects 1 to 3, wherein the bus converter means has a means for correcting any error that occurs in the reading of the sound signal.
The invention of aspect 8 is equivalent to the invention of aspect 4, provided that it is expressed as a method of controlling an automotive audio system which is a modification of the invention recited in any one of aspects 5 to 7, which further includes the step of correcting any error that occurs in the reading of the sound signal in the second unit.
According to the inventions of aspects 4 and 8, errors are corrected by the bus converter means and other relevant components of the second unit; therefore, even if an error in the reading of sound signal occurs due, for example, to a flaw in the medium or its vibration, relevant information such as the occurrence of the flaw and the contents of its correction can be recognized in the bus converter means and the main unit. As a result, error correction can be performed in diverse ways by various components of the system and its operational stability is improved, leading to particularly great benefits when successive errors occur. If the configuration according to aspects 4 and 8 is combined with the command resolving means and step recited in aspects 3 and 7, the second unit needs only to send a control signal such as one for replay start or track-up to the first unit, which then executes the necessary steps including designation of a new start address and error correction; as a result, the burden on the second unit is reduced.